1. Field of the Invention
This invention relates to a semiconductor device having fin FETs (Field Effect Transistors) and a manufacturing method thereof.
2. Description of the Related Art
Fin FETs, particularly, fin FETs formed on a bulk Si substrate are devices which are low in cost and excellent in the cut-off characteristic and are regarded as favorable next-generation transistor structures (for example, refer to Jpn. Pat. Appln. KOKAI Publication No. 2005-229107).
However, in order to attain the multiple threshold voltages and cope with analog devices, since the planar device is simple in structure and low in cost, it is necessary to mount the conventional planar MOSFETs and fin FETs together on the actual LSI. Therefore, a simple manufacturing process for mounting both of the FETs together is required.
If planar MOSFETs and fin FETs are mounted together on one chip, the surfaces of the gates become irregular and there occurs a problem that it becomes difficult to perform the lithography process for formation of minute gates and it becomes impossible to simultaneously process the gates of the fin region and planar region. Further, there occurs a problem that the number of manufacturing steps increases and the manufacturing cost rises.